Modification variability

Modification (phenotypic) variability- changes in the body associated with a change in the phenotype due to the influence environment and are, in most cases, adaptive in nature. The genotype does not change. Generally modern concept"adaptive modifications" corresponds to the concept of "certain variability" introduced into science by Charles Darwin.

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Conditional classification of modification variability

According to the changing signs of the body:
- morphological changes
- physiological and biochemical adaptations - homeostasis (increase in the level of red blood cells in the mountains, etc.)
By the range of the reaction norm
- narrow (more characteristic of qualitative traits)
- wide (more typical for quantitative traits)
By value:
- modifications (beneficial to the body - appear as an adaptive reaction to environmental conditions)
- morphoses (non-hereditary changes in the phenotype under the influence of extreme environmental factors or modifications that occur as an expression of newly emerging mutations that do not have an adaptive nature)
- phenocopies (various non-hereditary changes that copy the manifestation of various mutations)
By duration:
- there is only an individual or group of individuals that have been influenced by the environment (not inherited)
- long-term modifications - last for two or three generations

The mechanism of modification variability

Environment as a reason for modifications

Modification variability is not the result of changes in the genotype, but of its response to environmental conditions. With modification variability, the hereditary material does not change, the expression of genes changes.

Under the influence of certain environmental conditions on the body, the course of enzymatic reactions (enzyme activity) changes and specialized enzymes can be synthesized, some of which (MAP kinase, etc.) are responsible for the regulation of gene transcription, depending on changes in the environment. Thus, environmental factors are able to regulate gene expression, that is, the intensity of their production of specific proteins, the functions of which correspond to specific environmental factors.

Melanin is produced by four genes located on different chromosomes. Nai large quantity dominant alleles of these genes - 8 - is found in people of the Negroid race. When exposed to a specific environment, such as intense exposure ultraviolet rays, epidermal cells are destroyed, which leads to the release of endothelin-1 and eicosanoids. They cause the activation of the tyrosinase enzyme and its biosynthesis. Tyrosinase, in turn, catalyzes the oxidation of the amino acid tyrosine. Further formation of melanin takes place without the participation of enzymes, however, a larger amount of the enzyme causes more intense pigmentation.

reaction rate

The limit of manifestation of the modification variability of an organism with an unchanged genotype is the norm reaction. The reaction rate is determined by the genotype and varies in different individuals of a given species. In fact, the reaction rate is a range of possible levels of gene expression, from which the expression level that is most suitable for given environmental conditions is selected. The reaction rate has limits or boundaries for each species(lower and upper) - for example, increased feeding will lead to an increase in the mass of the animal, however, it will be within the normal range of the reaction characteristic of this species or breed. The reaction rate is genetically determined and inherited. For different signs reaction limits vary greatly. For example, the value of milk yield, the productivity of cereals and many other quantitative traits have wide limits of the reaction norm, narrow limits - the color intensity of most animals and many other qualitative traits.

However, some quantitative traits are characterized by a narrow reaction rate (fat content of milk, number of toes in guinea pigs), and for some qualitative characters - wide (for example, seasonal color changes in many animal species of northern latitudes). In addition, the boundary between quantitative and qualitative features is sometimes very arbitrary.

Characteristics of modification variability

reversibility - changes disappear when the specific environmental conditions that provoked them change
group character
changes in the phenotype are not inherited, the norm of the genotype reaction is inherited
statistical regularity of variation series
affects the phenotype without affecting the genotype itself.

Analysis and patterns of modification variability

Variation series

A ranked display of the manifestation of modification variability - a variation series - a series of modification variability of an organism's property, which consists of individual modifications placed in order of increasing or decreasing quantitative expression of the property (leaf size, change in coat color intensity, etc.). A single indicator of the ratio of two factors in a variation series (for example, the length of the coat and the intensity of its pigmentation) is called variant. For example, wheat growing in one field can vary greatly in the number of ears and spikelets due to different soil indicators and moisture in the field. Compiling the number of spikelets in one spike and the number of ears, you can get a variation series in a statistical form:

Variation curve

A graphical representation of the manifestation of modification variability - a variation curve - displays both the range of property variation and the frequency of individual variants. It can be seen from the curve that the average variants of the manifestation of the trait are most common (Quetelet's law). The reason for this, apparently, is the effect of environmental factors on the course of ontogeny. Some factors suppress gene expression, while others, on the contrary, increase it. Almost always, these factors, simultaneously acting on ontogeny, neutralize each other, that is, neither a decrease nor an increase in the value of a trait is observed. This is the reason why individuals with extreme expressions of the trait are found in much smaller numbers than individuals with an average value. For example, the average height of a man - 175 cm - is most common in European populations.

When constructing a variation curve, you can calculate the value of the standard deviation and, on the basis of this, build a graph of the standard deviation from the median - the most common feature value.

Modification variability in the theory of evolution

Darwinism

In 1859, Charles Darwin published his work on the subject of evolution entitled The Origin of Species by Natural Selection, or the Maintenance of Favorable Races in the Struggle for Life. In it, Darwin showed the gradual development of organisms as a result of natural selection. Natural selection consists of the following mechanism:

first, an individual appears with new, completely random properties (formed as a result of mutations)
then she is or is not able to leave offspring, depending on these properties
finally, if the outcome of the previous stage is positive, then it leaves offspring and its descendants inherit the newly acquired properties

New properties of an individual are formed as a result of hereditary and modification variability. And if hereditary variability is characterized by a change in the genotype and these changes are inherited, then with modification variability, the ability of the genotype of organisms to change the phenotype when exposed to the environment is inherited. With constant exposure to the same environmental conditions on the genotype, mutations can be selected, whose effect is similar to the manifestation of modifications, and, thus, modification variability turns into hereditary variability (genetic assimilation of modifications). An example is the constant high percentage of melanin pigment in the skin of the Negroid and Mongoloid races compared to the Caucasoid.

Darwin called modification variability definite (group).

A certain variability is manifested in all normal individuals of the species, subjected to a certain influence. A certain variability expands the limits of the existence and reproduction of the organism.

Natural selection and modification variability

Stabilizing selection is characterized by the neutralization of mutations and the formation of a reserve of these mutations, which leads to the development of the genotype with a constant phenotype. As a result, organisms average rate reactions dominate under constant conditions of existence. For example, generative plants retain the shape and size of a flower that matches the shape and size of the insect that pollinates the plant.

Disruptive selection is characterized by the discovery of reserves with neutralized mutations and the subsequent selection of these mutations to form a new genotype and phenotype that are suitable for the environment. As a result, organisms with an extreme rate of reaction survive. For example, insects with strong wings are more resistant to gusts of wind, while insects of the same species with weak wings are blown away.

Driving selection is characterized by the same mechanism as disruptive selection, but it is aimed at the formation of a new average reaction norm. For example, insects develop resistance to chemicals.

Epigenetic theory of evolution

According to the main provisions of the epigenetic theory of evolution, published in 1987, the substrate for evolution is a holistic phenotype - that is, morphoses in the development of an organism are determined by the influence of environmental conditions on its ontogeny (epigenetic system). At the same time, a stable developmental trajectory based on morphoses (creod) is formed - a stable epigenetic system is formed that is adaptive to morphoses. This system of development is based on the genetic assimilation of organisms (modification genocopy), which consists in the correspondence of any modification to a certain mutation. That is, it means that a change in the activity of a particular gene can be caused by both a change in the environment and a certain mutation. Under the action of a new environment on the body, mutations are selected that adapt the body to new conditions, so the body, first adapting to the environment with the help of modifications, then becomes adapted to it genetically (motor selection) - a new genotype arises, on the basis of which a new phenotype. For example, with congenital underdevelopment of the motor apparatus of animals, a restructuring of the supporting and motor organs occurs in such a way that underdevelopment turns out to be adaptive. Further, this trait is fixed by hereditarily stabilizing selection. Subsequently, a new mechanism of behavior appears, aimed at adapting to adaptation. Thus, in the epigenetic theory of evolution, postembryonic morphosis based on special environmental conditions is considered as the driving lever of evolution. Thus, natural selection in the epigenetic theory of evolution consists of the following stages:

Thus, the synthetic and epigenetic theories of evolution are quite different. However, there may be cases that are a synthesis of these theories - for example, the appearance of morphoses due to the accumulation of neutral mutations in reserves is part of the mechanism of both synthetic (mutations appear in the phenotype) and epigenetic (morphoses can lead to genocopy of modifications if the original mutations did not determine this ) theories.

Forms of modification variability

In most cases, modification variability contributes to a positive adaptation of organisms to environmental conditions - the reaction of the genotype to the environment improves and a rearrangement of the phenotype occurs (for example, the number of erythrocytes in a person who climbs mountains increases). However, sometimes, under the influence of adverse environmental factors, for example, the influence of teratogenic factors on pregnant women, phenotype changes occur that are similar to mutations (not hereditary changes similar to hereditary ones) - phenocopies. Also, under the influence of extreme environmental factors, morphoses may appear in organisms (for example, a disorder of the motor apparatus due to injury). Morphoses are irreversible and non-adaptive in nature, and in the labile nature, the manifestations are similar to spontaneous mutations. Morphoses are accepted by the epigenetic theory of evolution as the main factor in evolution.

Long-term modification variability

In most cases, modification variability is non-hereditary in nature and is only a reaction of the genotype of a given individual to environmental conditions, followed by a change in the phenotype. However, long-term modifications are also known, which have been described in some bacteria, protozoa, and multicellular eukaryotes. To understand the possible mechanism of long-term modification variability, let us first consider the concept of a genetic trigger.

For example, bacterial operons contain, in addition to structural genes, two sections - a promoter and an operator. The operator of some operons is located between the promoter and structural genes (in others, it is part of the promoter). If the operator is bound to a protein called a repressor, then together they prevent RNA polymerase from moving along the DNA chain. In bacteria E. coli a similar mechanism can be observed. With a lack of lactose and an excess of glucose, a repressor protein (Lacl) is produced, which attaches to the operator, preventing RNA polymerase from synthesizing mRNA for translation of the enzyme that breaks down lactose. However, when lactose enters the bacterial cytoplasm, lactose (an inducer substance) attaches to the repressor protein, changing its conformation, which leads to dissociation of the repressor from the operator. This causes the beginning of the synthesis of an enzyme for the breakdown of lactose.

In bacteria, when dividing, an inductor substance (in the case of E. coli- lactose) is transferred to the cytoplasm of the daughter cell and triggers the dissociation of the repressor protein from the operator, which entails the manifestation of the activity of the enzyme (lactase) to cleave lactose in sticks even in the absence of this disaccharide in the medium.

If there are two operons and if they are interconnected (the structural gene of the first operon encodes a repressor protein for the second operon and vice versa), they form a system called a trigger. When the first operon is active, the second one is disabled. However, under the influence of the environment, the synthesis of the repressor protein by the first operon can be blocked, and then the trigger switches: the second operon becomes active. This trigger state can be inherited by subsequent generations of bacteria. Molecular triggers can provide long-term modifications in eukaryotes as well. This can occur, for example, by cytoplasmic inheritance of cytoplasmic inclusions in bacteria during their reproduction.

The effect of trigger switching can be observed in non-cellular life forms, such as bacteriophages. When introduced into a cell, bacteria with a lack of nutrients they remain inactive, invading the genetic material. When favorable conditions appear in the cell, phages multiply and break out of the bacterium - a trigger switch occurs due to a change in the environment.

Cytoplasmic inheritance

Comparative characteristics of the forms of variability

Comparative characteristics forms of variability

Property	Non-hereditary (adaptive modifications)	hereditary
Object of change	Phenotype in the reaction range	Genotype
Occurrence factor	Changes in environmental conditions	Gene recombination due to gamete fusion, crossing over, mutation
Property Inheritance	Not inherited	Inherited
Values for an individual	Increases vitality, adaptability to environmental conditions	Beneficial changes lead to survival, harmful - to the death of the organism.
View value	Promotes survival	Leads to the emergence of new populations, species as a result of divergence
Role in evolution	Adaptation of organisms to environmental conditions	Material for natural selection
Shape of variability	group	Individual
regularity	Statistical regularity of variation series	Law of homologous series of hereditary variability

Together, hereditary and modificational variation provide the basis for natural selection. At the same time, qualitative or quantitative changes in the manifestations of the genotype in the signs of the phenotype (hereditary variability) determine the result of natural selection - the survival or death of the individual.

Modification variability in human life

The practical use of the patterns of modification variability is of great importance in plant growing and animal husbandry, as it makes it possible to foresee and plan in advance the maximum use of the capabilities of each plant variety and animal breed (for example, individual indicators of a sufficient amount of light for each plant). Creation of known optimal conditions for the implementation of the genotype ensures their high productivity.

It also makes it possible to expediently use the child’s innate abilities and develop them from childhood - this is the task of psychologists and teachers who, even at school age, are trying to determine the inclinations of children and their abilities for one or another professional activity, increasing the level of implementation of genetically determined children's abilities.

There are two main types variability living organisms: hereditary and non-hereditary. The first can be mutational and combinative. The second is called modification variability. It includes changes in traits that are not preserved during sexual reproduction, since these changes do not affect the genotype. She is also called phenotypic variability.

Modification variability arises as a result of the interaction of organisms with the environment, i.e. in the process of realization of genetic information. Different organisms react differently to environmental factors. There is such a thing as the reaction rate. These are the limits of modification variability, which are determined by the capabilities of a given genotype.

characteristic feature modifications is that the same impact causes the same change in all individuals that have been subjected to it. For this reason, Charles Darwin called modification variability definite. Modifications are especially good to observe in individuals identical in genotype, but placed in different habitat conditions. Thus, significant differences in many characteristics are manifested in plants of the same species growing in mountainous and valley conditions. In the mountains, plants are usually squat, with short stems, basal leaves, deep roots; in the valley, the plants are higher, their root system located closer to the soil surface. When plants are moved to another habitat, the modifications disappear. Plant modifications that occur under the influence of different lighting, sowing density, and changes in nutrition are well known.

Modifications in animals are no less diverse. There are known changes in the physique of fish depending on the nature of the reservoir. So, for example, in lakes and slow rivers (i.e. in large reservoirs), crucian carp are larger and more rounded. In ponds and small swampy lakes, the fish are much smaller, and their body is elongated.

In chickens, under the influence of the length of daylight hours, egg production changes; big cattle and horses with great physical exertion, muscle volume, lung volume increase, blood circulation increases.

Of particular interest is the modification variability in humans. To evaluate it, a very effective twin method. Studies performed on twins have demonstrated the enormous role of heredity in the development of the body. Identical twins raised in different conditions, have a striking physical and psychological similarity, although differences in education, of course, leave an imprint on their intellectual abilities and behavior.

In most cases, modification is a useful adaptive reaction of the organism, i.e. is adaptive. Plants growing in the shade have a large leaf blade to maximize the capture solar energy. In arid areas, plants, on the contrary, reduce the leaf blade, the number of stomata decreases, the epidermis thickens, i.e. signs appear that protect plants from moisture loss.

Color change in many insects, fish, amphibians, depending on the habitat or has protective function or, conversely, helps to lie in wait for prey. In humans, sunburn is a protective reaction against insolation.

The adaptive nature is usually inherent in modifications that are caused by exposure to ordinary environmental factors. If the organism falls under the action of an unusual factor, or the intensity of the usual one sharply increases, then non-adaptive modifications may occur, often having the character of deformities. Such changes are called morphoses. They often occur under the influence of chemicals and radiation. For example, when seeds are irradiated, seedlings grow out of them with shriveled leaves, with cotyledons of different shapes, with an uneven green color. In Drosophila, when irradiated, real monsters sometimes develop.

In plants, morphoses often occur as a result of an excess or lack of a substance in the soil, most often a trace element. So, a lack of copper causes a strong tillering of cereals. At the same time, the inflorescences do not come out of the leaf wrappers and dry out. In fish fry developing in water with an admixture of lithium chloride, only one eye located in the middle is formed.

Some modifications that occur under the influence of radiation, extreme temperatures and other potent factors mimic specific mutations. Thus, under the influence of temperature shock to which Drosophila pupae were subjected, flies with curved wings, wing notches, and short wings appeared, indistinguishable from flies of some mutant lines. Such modifications are called phenocopies.

The adaptive nature of modifications is due to the norm of the genotype reaction, which allows the trait to change without disturbing the structure of the corresponding gene (i.e., without mutation). The wider the reaction rate, the higher the adaptive potential of an individual, population or species.

Unlike mutations, modifications have varying degrees of persistence. Many modifications disappear shortly after the factor that caused them (for example, sunburn) ceases to act. Others may persist throughout the life of the individual. For example, people who have been ill with rickets in childhood due to a lack of vitamin D can remain bow-legged for life.

Sometimes there is an aftereffect of modifications. So, in mammals, offspring born by an emaciated mother are smaller and weaker than normal ones. However, this influence quickly disappears if the factor that caused the modification in the mother is eliminated.

Very rarely, modifications persist for several generations. This is observed only during vegetative or parthenogenetic reproduction. Long-term modifications have been described in unicellular algae and protozoa. For example, resistance to high concentrations of arsenic in the shoe ciliates persisted for 10.5 months, after which it decreased to the initial level. The mechanism of long-term modifications is not entirely clear.

Abstract on the topic:

Modification variability

Abstract completed

11th grade student a

Sagiev Alexander

Modification (phenotypic) variability- changes in the body associated with a change in the phenotype due to the influence of the environment and, in most cases, are adaptive in nature.

The genotype does not change. In general, the modern concept of “adaptive modifications” corresponds to the concept of “certain variability”, which was introduced into science by Charles Darwin.

Conditional classification of modification variability

According to the changing signs of the body:

1) morphological changes

2) physiological and biochemical adaptations - homeostasis (increase in the level of red blood cells in the mountains, etc.)

According to the range of the reaction norm:

1) narrow (more typical for qualitative features)

2) wide (more typical for quantitative traits)

By value:

1) modifications (beneficial for the body - appear as an adaptive reaction to environmental conditions)

2) morphoses (non-hereditary changes in the phenotype under the influence of extreme environmental factors or modifications that occur as an expression of newly emerging mutations that do not have an adaptive character)

3) phenocopies (various non-hereditary changes that copy the manifestation of various mutations) - a type of morphosis

By duration:

1) there is only an individual or a group of individuals that have been influenced by the environment (not inherited)

2) long-term modifications - last for two or three generations

Characteristics of modification variability

1) reversibility - changes disappear when the specific environmental conditions that provoked them change

2) group character

3) changes in the phenotype are not inherited, the norm of the genotype reaction is inherited

4) statistical regularity of variation series

5) affects the phenotype, while not affecting the genotype itself

The mechanism of modification variability

1) Environment as the reason for modifications

Under the influence certain conditions environment, the course of enzymatic reactions (enzyme activity) changes and the synthesis of specialized enzymes can occur, some of which (MAP kinase, etc.) are responsible for the regulation of gene transcription, depending on environmental changes. Thus, environmental factors are able to regulate gene expression, that is, the intensity of their production of specific proteins, the functions of which correspond to specific environmental factors. For example, four genes that are located on different chromosomes are responsible for the production of melanin. The largest number of dominant alleles of these genes - 8 - is found in people of the Negroid race. When exposed to a specific environment, such as intense exposure to ultraviolet rays, epidermal cells are destroyed, which leads to the release of endothelin-1 and eicosanoids. They cause the activation of the tyrosinase enzyme and its biosynthesis. Tyrosinase, in turn, catalyzes the oxidation of the amino acid tyrosine. Further formation of melanin takes place without the participation of enzymes, however, a larger amount of the enzyme causes more intense pigmentation.

2) Reaction rate

The limit of manifestation of the modification variability of an organism with an unchanged genotype is the reaction norm. The reaction rate is determined by the genotype and varies in different individuals of a given species. In fact, the reaction rate is a range of possible levels of gene expression, from which the expression level that is most suitable for given environmental conditions is selected. The reaction rate has a limit for each species - for example, increased feeding will lead to an increase in the animal's weight, but it will be within the reaction rate characteristic of a given species or breed. The reaction rate is genetically determined and inherited.

For different changes there are different limits of the reaction norm. For example, the amount of milk yield, the productivity of cereals vary greatly (quantitative changes), the color intensity of animals varies slightly, etc. (qualitative changes). In accordance with this, the reaction rate can be wide (quantitative changes - the size of the leaves of many plants, the body size of many insects, depending on the feeding conditions of their larvae) and narrow (qualitative changes - the color of the pupae and adults of some butterflies). However, some quantitative traits are characterized by a narrow reaction rate (fat content of milk, number of toes in guinea pigs), while some qualitative traits are characterized by a wide reaction rate (for example, seasonal color changes in many animal species of northern latitudes).

Analysis and patterns of modification variability

1) Variation row

Ranked display of the manifestation of modification variability - a variation series - a series of modification variability of an organism's property, which consists of individual properties of modifications, placed in order of increase or decrease in the quantitative expression of the property (leaf size, change in coat color intensity, etc.). A single indicator of the ratio of two factors in a variation series (for example, the length of the coat and the intensity of its pigmentation) is called a variant. For example, wheat growing in one field can vary greatly in the number of ears and spikelets due to different soil indicators and moisture in the field. Compiling the number of spikelets in one spike and the number of ears, you can get a variation series in a statistical form:

Variation series of modification variability of wheat

2) Variation curve

Graph of the standard deviation coming from the variation curve "modification variability of wheat"

Modification variability in the theory of evolution

1) Darwinism

In 1859, Charles Darwin published his work on the subject of evolution entitled The Origin of Species by Means of Natural Selection, or the Preservation of Favorable Races in the Struggle for Life. In it, Darwin showed the gradual development of organisms as a result of natural selection.

Natural selection consists of the following mechanism:

1) first an individual appears with new, completely random properties (formed as a result of mutations)

2) then she is or is not able to leave offspring, depending on these properties

3) finally, if the outcome of the previous stage is positive, then it leaves offspring and its descendants inherit the newly acquired properties

2) Natural selection and modification variability

Modification variability is closely related to natural selection. Natural selection has four directions, three of which are directly aimed at the survival of organisms with different forms of non-hereditary variability. It is stabilizing, moving and disruptive selection. Stabilizing selection is characterized by the neutralization of mutations and the formation of a reserve of these mutations, which leads to the development of the genotype with a constant phenotype. As a result, organisms with an average rate of reaction dominate under constant conditions of existence. For example, generative plants retain the shape and size of a flower that matches the shape and size of the insect that pollinates the plant. Disruptive selection is characterized by the discovery of reserves with neutralized mutations and the subsequent selection of these mutations to form a new genotype and phenotype that are suitable for the environment. As a result, organisms with an extreme rate of reaction survive. For example, insects with large wings are more resistant to gusts of wind, while insects of the same species with weak wings are blown away. Driving selection is characterized by the same mechanism as disruptive selection, but it is aimed at the formation of a new average reaction norm. For example, insects develop resistance to chemicals.

We know that modification variability is a special case of non-hereditary variability.

Modification variability - ability of organisms with the same genotype develop differently in different environmental conditions. In a population of such organisms, a certain set of phenotypes. However, the organisms must be the same age.

Modifications - these are phenotypic non-hereditary differences arising under the influence of environmental conditions in organisms of the same genotype (Karl Naegeli, 1884).

Modification examples widely known and numerous.

The morphology of the leaves water buttercup and arrowhead depends on what environment, air or underwater, they develop.

arrowhead (Sagittaria sagittaefolia) has different leaves: arrow-shaped (surface), heart-shaped (floating) and ribbon-shaped (underwater). Consequently, the arrowhead does not have a certain leaf shape that is hereditarily determined, but the ability to change this shape within certain limits depending on the conditions of existence, which is adaptive feature organism.

If the aerial part of the stem potatoes artificially shut out the light, tubers hanging in the air develop on it.

At flounders , leading a benthic lifestyle, the upper side of the body is dark, which makes it invisible to approaching prey, and the lower side is light. But if the aquarium has a glass bottom and is illuminated not from above, but from below, then the lower surface of the body becomes dark.

Ermine rabbits have white fur on the body, except for the end of the muzzle, paws, tail and ears. If you shave an area, for example, on the back and keep the animal at a low temperature (0-1 ° C), then black hair grows on the shaved place. If you pluck out some of the black hair and place the rabbit in conditions of elevated temperature, then white hair grows again.

This is due to the fact that each part of the body is characterized by its own level of blood circulation and, accordingly, the temperature, depending on which the black pigment is formed or degraded - melanin . The genotype remains the same.

Wherewarmly , where the pigment degrades →white coat color wherecold (distal areas), where the pigment does not degrade →black wool.

Mod Properties

S. M. Gershenzon describes the following modification properties :

1. The degree of severity of the modification proportional to strength and duration effect on the body of a factor that causes modification. This regularity radically distinguishes modifications from mutations, especially gene ones.

2. In the vast majority of cases, the modification is useful adaptive reaction organism to one or another external factor. This can be seen in the example of the above modifications in various organisms.

3. Only those modifications that are caused by normal changes in nature these conditions , With which this species faced many times before. If the body enters unusual , extreme circumstances , then there are modifications devoid of adaptive meaning - morphoses .

If act on larvae or pupae Drosophila X-ray or ultraviolet rays, as well as the maximum tolerated temperature, then developing flies show a variety of morphoses ( flies with upcurled wings, with notches on the wings, with spread wings, with wings of small size, phenotypically indistinguishable from flies of several mutant lines of Drosophila).

4. Unlike mutations, modifications reversible , i.e. the change that has arisen gradually disappears if the effect that caused it is eliminated. So, a person’s tan disappears when the skin ceases to be exposed to insolation, the volume of muscles decreases after the cessation of training, etc.

5. Unlike mutations, modifications are not inherited . This position has been most acutely discussed throughout the history of mankind. Lamarck believed that any changes in the body can be inherited, acquired during life (Lamarckism). Even Darwin recognized the possibility of inheritance of some modification changes.

The first serious blow to the idea of the inheritance of acquired traits came from A. Weisman . For 22 generations, he chopped off the tails of white mice and crossed them with each other. A total of 1,592 mice were examined, and no shortening of the tail was found in newborn mice. The results of the experiment were published in 1913, but there was no particular need for it, since intentional injury to humans, made for ritual or "aesthetic" reasons - circumcision, ear piercing, mutilation of the feet, skull, etc., are also known not to be inherited.

In the USSR in the 30-50s. erroneous theories have become widespread Lysenko about the inheritance of "acquired characteristics", that is, in fact, modifications. Many experiments carried out on different organisms have shown the non-heritability of modifications, and studies of this kind are now only historical interest. In 1956-1970. F. Creek formulated the so-called "the central dogma of molecular biology" , according to which the transfer of information is possible only from DNA to proteins, but not in the opposite direction.

Non-hereditary (phenotypic) variability is not associated with a change in genetic material. It is the body's response to specific changes in the environment. The study of the influence of new conditions on a person showed that such signs as the type of metabolism, predisposition to certain diseases, blood type, skin patterns on the fingers and others are determined by the genotype and their expression depends little on environmental factors. Other characteristics, such as intelligence, weight, height, etc., have a wide range of changes, and their manifestation is largely determined by the environment. Those external differences that are caused by the environment are called modifications. Modifications are not associated with a change in the genetic structures of an individual, but are only a particular reaction of the genotype to specific changes in the environment (temperature, oxygen content in the inhaled air, the nature of nutrition, education, training, etc.). However, the limits of these trait changes in response to environmental influences are determined by the genotype. Specific changes are not inherited, they are formed during the life of an individual. The genotype is inherited with its specific rate of reaction to a change in the environment. Thus, the set of traits of an individual (its phenotype) is the result of the implementation of genetic information in specific environmental conditions. The phenotype is formed in the process individual development starting from the moment of fertilization. The physical, mental and mental health of a person is the result of the interaction of the characteristics inherited by a person with environmental factors that affect him throughout his life. Neither heredity nor the human environment is immutable. This important principle underlies the modern understanding of the processes of variation and heredity. There are no two people in the world, except for identical twins (developing from the same fertilized egg) that have the same set of genes. It is also impossible to find two people who have lived their lives in the same conditions. Heredity and environment are not opposed to each other: they are one and inconceivable one without the other.

Modification variability

Among various types variability discussed above, non-hereditary variability, which is also called modification variability, was singled out. The general patterns of variability are known much worse than the laws of inheritance.

Modification variability is phenotypic differences in genetically identical individuals.

External influences can cause changes in an individual or a group of individuals that are harmful, indifferent or beneficial for them, i.e. adapted.

As you know, the evolutionary theory developed by J.B. Lamarck (1744-1829), was based on the erroneous postulate of the inheritance of changes acquired during life, i.e. about modification inheritance. In itself, the representation of J.B. Lamarck on the evolution of organic forms was undoubtedly progressive for his time, but his explanation of the mechanism of evolutionary progress was incorrect and reflected a common misunderstanding characteristic of eighteenth-century biologists.

C. Darwin (1809-1882) in his "Origin of Species ..." divided variability into certain and indefinite. This classification generally corresponds to the current division of variability into non-hereditary and hereditary.

One of the first researchers who studied modification variability was K. Naegeli (1865), who reported that if alpine forms of plants, such as hawksbill, are transferred to the rich soil of the Munich Botanical Garden, then they show an increase in power, abundant flowering, and some plants change beyond recognition. If the forms are again transferred to the poor rocky soils, then they return to their original form. Despite the results obtained, K. Naegeli remained a supporter of the inheritance of acquired properties.

For the first time, a rigorous quantitative approach to the study of modification variability from the standpoint of genetics was applied by V. Johansen. He studied the inheritance of the weight and size of bean seeds, traits that largely change under the influence of both genetic factors and plant growing conditions.

A. Weisman (1833-1914) was a staunch opponent of the inheritance of properties acquired in ontogenesis. Consistently defending the Darwinian principle of natural selection as the driving force of evolution, he proposed to separate the concepts somatogenic and blastogenic changes, i.e. changes in the properties of somatic cells and organs, on the one hand, and changes in the properties of generative cells, on the other. A. Weisman pointed out the impossibility of the existence of a mechanism that would transfer changes in somatic cells to sex in such a way that in the next generation the organisms would change adequately to those modifications that the parents underwent during their ontogenesis.

Illustrating this situation, A. Weisman set up the following experiment, which proved the non-inheritance of acquired traits. For 22 generations, he cut off the tails of white mice and crossed them with each other. In total, he examined 1592 individuals and never found shortening of the tail in newborn mice.

Types of modification variability

Distinguish age, seasonal and environmental modifications. They come down to changing only the degree of expression of the trait; violation of the structure of the genotype does not occur with them. It should be noted that it is impossible to draw a clear boundary between age, seasonal, and ecological modifications.

Age , or ontogenetic, modifications are expressed as a constant change of characters in the process of development of an individual. This is clearly demonstrated by the example of the ontogeny of amphibians (tadpoles, underyearlings, adults), insects (larva, pupa, adults) and other animals, as well as plants. In humans, in the process of development, modifications of morphophysiological and mental signs are observed. For example, a child will not be able to develop properly both physically and intellectually if early childhood it will not be influenced by normal external, including social, factors. For example, a long stay of a child in a socially disadvantaged environment can cause an irreversible defect in his intelligence.

Ontogenetic variability, like ontogeny itself, is determined by the genotype, where the development program of the individual is encoded. However, the features of the formation of the phenotype in ontogeny are due to the interaction of the genotype and the environment. Under the influence of unusual external factors, deviations in the formation of a normal phenotype may occur.

Seasonal modifications , individuals or entire populations are manifested in the form of a genetically determined change in traits (for example, a change in coat color, the appearance of a down in animals), which occurs as a result of seasonal changes in climatic conditions [Kaminskaya E.A.].

A striking example of such variability is the experiment with the ermine rabbit. In the ermine rabbit, a certain area is shaved bald on the back (the back of the ermine rabbit is normally covered with white wool) and then the rabbit is placed in the cold. It turns out that in this case, a dark-pigmented hair appears on a bare spot, exposed to low temperature, and as a result, on the back - dark spot. It is obvious that the development of one or another sign of a rabbit is his phenotype, in this case, ermine coloration, depends not only on its genotype, but also on the entire set of conditions in which this development occurs.

The Soviet biologist Ilyin showed that the ambient temperature has more value in the development of pigment in the ermine rabbit, and for each area of the body there is a temperature threshold, above which white hair grows, and below - black (Fig. 1).

Fig. 1. Map of temperature thresholds of wool pigmentation in the ermine rabbit (from Ilyin according to S.M. Gershenzon, 1983)

Seasonal modifications can be attributed to the group environmental modifications. The latter are adaptive changes in the phenotype in response to changes in environmental conditions. Ecological modifications are phenotypically manifested in a change in the degree of expression of a trait. They can appear early in development and persist throughout life. An example is the various forms of the leaf of the arrowhead, due to the influence of the environment: arrow-shaped surface, wide floating, ribbon-shaped underwater.

An arrowhead plant that produces three types of leaves: underwater, floating and above water. Photo: Udo Schmidt

Environmental modifications affect quantitative (number of petals in a flower, offspring of animals, weight of animals, plant height, leaf size, etc.) and qualitative (flower color in lungwort, forest rank, primrose; human skin color under the influence of ultraviolet rays, etc.). ) signs. So, for example, Levakovsky, when growing a blackberry branch in water until it blooms, found significant changes in the anatomical structure of its tissue. In a similar experiment, Constantin revealed phenotypic differences in the structure of the surface and underwater parts of the leaf in buttercup.

Rice. Water ranunculus leaves and a frog :) Photo: Radio Tonreg

In 1895, the French botanist G. Bonnier conducted an experiment that became classic example ecological modification. He divided one dandelion plant into two parts and grew them in different conditions: on the plain and high in the mountains. The first plant reached normal height, and the second turned out to be dwarfed. Such changes occur in animals as well. For example, R. Wolterk in 1909 observed changes in the height of the helmet in Daphnia depending on feeding conditions.

Ecological modifications, as a rule, are reversible by them with a change of generations, provided that changes in the external environment can manifest themselves. For example, the offspring of low-growing plants on well-fertilized soils will be of normal height; a certain number of petals in the flower of a plant may not be repeated in the offspring; a person with crooked legs due to rickets has quite normal offspring. If the conditions do not change over a number of generations, the degree of expression of the trait in the offspring is preserved, it is often mistaken for a persistent hereditary trait (long-term modifications).

With the intensive action of many agents, non-heritable changes are observed, random (in their manifestation) in relation to the effect. Such changes are called morphoses. Very often they resemble the phenotypic manifestation of known mutations. Then they are called phenocopies these mutations. In the late 30s - early 40s, I.A. Rapoport investigated the effects of many chemical compounds on Drosophila, showing that, for example, antimony compounds are brown (brown eyes); arsenic acid and some other compounds - changes in wings, body pigmentation; boron compounds - eyeless (eyelessness), aristopredia (turning aristas into legs), silver compounds - yellow (yellow body), etc. At the same time, some morphoses, when exposed to a certain stage of development, were induced with high frequency(up to 100%).

Characteristics of modification variability:

1. Adaptive changes (example, arrowhead).

2. Adaptive character. This means that in response to changing environmental conditions, an individual exhibits such phenotypic changes that contribute to their survival. An example is the change in the moisture content in the leaves of plants in arid and humid regions, the color of a chameleon, the shape of a leaf in an arrowhead, depending on environmental conditions.

3. Reversibility within one generation, i.e. with change external conditions in adults, the degree of expression of certain signs changes. for example, in cattle, depending on the conditions of detention, milk yield and fat content of milk may fluctuate, in chickens - egg production).

4. Modifications are adequate, i.e. the degree of manifestation of the symptom is directly dependent on the type and duration of the action of a particular factor. Thus, improving the maintenance of livestock contributes to an increase in the live weight of animals, fertility, milk yield and fat content of milk; on fertilized soils under optimal climatic conditions, the yield of grain crops increases, etc.

5. Mass character. Mass is due to the fact that the same factor causes approximately the same change in individuals that are genotypically similar.

6. Long term modifications. They were first described in 1913 by our compatriot V. Iollos. By irritating shoe ciliates, he caused them to develop a number of morphological features that persisted for a large number of generations, as long as reproduction was asexual. When the conditions of development change, long-term modifications are not inherited. Therefore, the opinion is erroneous that by upbringing and external influence it is possible to fix a new trait in the offspring. For example, it was assumed that from well-trained animals, offspring are obtained with better “acting” data than from untrained ones. The offspring of trained animals is indeed easier to educate, but this is explained by the fact that it inherits not the skills acquired by the parent individuals, but the ability to train, due to the inherited type of nervous activity.

7. Rate of reactions (modification limit). It is the reaction rate, and not the modifications themselves, that are inherited, i.e. the ability to develop one or another trait is inherited, and the form of its manifestation depends on the conditions of the external environment. The reaction rate is a specific quantitative and quality characteristics genotype, i.e. a certain combination of genes in the genotype and the nature of their interaction.

Table. Comparative characteristics of hereditary and non-hereditary variability

Property	Non-hereditary (adaptive modifications)	hereditary
Object of change	Phenotype in the reaction range	Genotype
Occurrence factor	Changes in environmental conditions	Gene recombination due to gamete fusion, crossing over, mutation
Property Inheritance	Not inherited	Inherited
Values for an individual	Increases vitality, adaptability to environmental conditions	Beneficial changes lead to survival, harmful - to the death of the organism.
View value	Promotes survival	Leads to the emergence of new populations, species as a result of divergence
Role in evolution	Adaptation of organisms to environmental conditions	Material for natural selection
Shape of variability	group	Individual
regularity	Statistical regularity of variation series	Law of homologous series of hereditary variability

Examples of modification variability

In a person:

An increase in the level of red blood cells when climbing mountains

Increased skin pigmentation with intense exposure to ultraviolet rays.

Development of the musculoskeletal system as a result of training

Scars (an example of morphosis).

In insects and other animals:

Color change in colorado potato beetle due to lasting influence on their pupae of high or low temperatures.

Change in coat color in some mammals when weather conditions change (for example, in a hare).

Different colors of nymphalid butterflies (for example, Araschnia levana) that developed at different temperatures.

In plants:

The different structure of underwater and surface leaves of the water buttercup, arrowhead, etc.

Development of undersized forms from seeds of lowland plants grown in the mountains.

In bacteria:

The work of the genes of the lactose operon of Escherichia coli (in the absence of glucose and in the presence of lactose, they synthesize enzymes for the processing of this carbohydrate).